This invention relates to a machinery unit with an heat barrier which separates a part that is hot during operation from a cool part of the machinery unit, while fastening means hold the two parts together and a flux of force is created between these parts through one or more force transmitting elements.
Published European Patent Application No. EP 731,280 discloses a unit of this type equipped with a heat barrier. This is a circulating pump unit for pumping hot fluids. The heat barrier serves to create a separation between the hot pump part and the parts of the unit which serve to seal and drive the pump. Such parts include, for example, the shaft seal and the rolling bearings; however, they might also comprise be the inner part of a magnetic clutch or of a gap tube motor in designs using no shaft seals.
While up to that time the overall length of the machinery unit had been increased by a considerable amount by a heat barrier, EP 731,280 achieved a definite reduction of the necessary axial length. This was achieved by the fact that, between the two parts of the unit, there is a rectilinear flux of force, this force flux passing through an insulating ceramic element or through a plurality of ceramic elements uniformly distributed about the circumference. Ceramic elements not only have the disadvantage of high price but also the disadvantage of their great mechanical frailty which requires special care and involves greater costs in handling.
It is the object of this invention to provide a machinery unit equipped with a heat barrier, which can be manufactured with the same axial length as a corresponding standardized machinery unit without a thermal barrier, but which avoids the need to use fragile and/or expensive materials.
Setting out from a machinery unit of the kind described above, the object is achieved according to the invention in that the hot part and the cool part have flange-like plates arranged adjacent to and spaced apart from one another, which are joined together via one or more force-transmitting metal elements, with the connection being made within a minimal cross-sectional area that is sufficient for the transmission of the force.
The force transmission which takes place through metal elements at first appears much less desirable than force transmission through ceramic elements which have a substantially lower thermal conductivity than metal. But since a metal element having only a small wall thickness is capable of transmitting comparatively great forces, the cross-sectional area available for thermal conduction can be kept substantially smaller with metal elements than it can in ceramic elements.
Due to the circumstance that, when metal is used, very strong walls can be made with very little thickness, configurations of the force-transmitting elements are possible which could not be achieved with ceramic. For example, profile bodies distributed over the circumference can be used which, unlike solid bodies made of ceramic, can also be made hollow. Likewise, one or more annular bodies made with relatively thin walls can serve as force-transmitting elements.
In the case of units held together by screws or bolts, it is especially advantageous if sleeves are used which surround the screws or bolts and have their ends in contact with the plates. But sleeves can also be used which extend into bores in the plates and are welded to the plates during assembly of the machinery unit. These have the additional advantage that manipulation that might cause any misalignment in the area of the thermal barrier can be largely avoided.
Different kinds of the possible force-transmitting elements can also be used in combination with each other.
The use of metal for the force-transmitting elements not only permits the use of elements which are independent of the plates, for example elements made of a material having a poor thermal conductivity, but also makes it possible to configure the force transmitting elements in one piece with one of the two plates.
If the two parts of the machinery unit that are joined together through the thermal barrier have a shaft passing through them, then it is recommended to connect the two plates together with a tubular body which surrounds and is spaced a slight distance from the shaft or a sleeve enclosing the shaft. In this case it is advantageous if the tubular body is joined in a pressure-tight and gas-tight manner to the plates. This can be achieved primarily by forming the tubular body on one of the two plates and welding it to the other plate.
It is furthermore recommendable to fill the space formed between the plates with a thermal insulating material.
Finally, it is also proposed to provide, in one or both plates, one or more annular cut-outs or recesses to accommodate force-transmitting elements and/or thermal insulating material. Such a measure serves primarily to shorten the axial length of the unit.